Method of making heat exchangers



Feb. 23, 1965 b. as. RIC-H METHOD 0F MAKING HEAT Origin-a1 Filed April 325, 11960 FIG. 3

INVENTOR DONALD G. RICH.

ATTORNEY.

1 3170 228 METHOD OF MAKINGHEAT EXCHANGERS Donald G.'Rich, Fayetteviile,rN.Y., assignoritofCarrier p Corporation, Syracuse, N.Y .,a corporation of Delaware;-

. Original appiication Apr. 25,1?60, Ser. No. 24,312, new a Patent No. 3,650,959, dated Aug. 28, W62. Divided and this application June 15,1962, Ser. 310,202,855 i 2 Claims. ((1l,29-'-].5'7.3) V e 1 This application is a division of'my copendin'g applica tion Serial No. 24,312, filed April 25, 1960, entitled Air Conditioning Apparatusilnow Patent No. 3,050,959 and States tubes below may not be-uniformly wetted. In or'dcr'to overcome this tendency, it is frequentpractice to spray a very large excess of liquid over'the heat exchange tubes reIatesto air conditioning-apparatus and,more partic ularly to air conditioning apparatus including heat exchangers of'the evaporative type. a p a The basicprinciple of Operation of a heat exchanger involves the'passage of two heat exchange mediums in relationship with each other such that heat is transmitted from one of the heat exchange mediums to the other. By way 'of example, a condenser in a standard refrigeration system may passcornpressed refrigerant gas through a series of pipes which form a heat exchanger. Air or water may be passed across the surface of'the pipesto remove heat from the compressed'gas and condense it to a liquid. Obviously, a heat exchanger of this type is limited; in its capacity by the temperature difference between theinternal fluid e.g,. refrigerant, and the external fluid elg., air. Another obvious limitation arises by reason of the fact that the temperature of air or other external heat ex changemedium which is passed across "the exterior surface of the heat exchange pipes rises dueto absorption of heat from the heat'exchanger and as more capacity is required, it is frequently necessaryto' increase'the volyurneof air which is passed by using fans or other means.

One of the well known techniques for increasing the capacity of a given size heat exchanger is to employ fins on the outside of the heat exchange tubes to increase the area available. for heat transfer.. Another method is to t and to collect the liquid which drips oif the tubes into a sump. This liquid is then pumped back -to the spray sys':

tem Where it is again discharged 'over' the surface of the heat exchange tubes. While this system produces'more' complete wetting of the heat exchange tubes, it introduces additional disadvantages. For example, the liquid from the spray system tends to become entrained'in the. 7

air surrounding the heat exchanger. If the heat exchanger is employedas a condenser on the top of alow building the entrained moisture frorn'the condenser may find its way to the street below where it is disagreeable to passersby. More serious, however, is the loss of liquid from the system and the necessity for maintaining an open sump over the heat exchanger to collect the excess liquid; The

open sump involves the" additional expense of a pump and other piping must be associated with itto return the liquid to the spray system: Furthermore, since heat exchangers or this type are frequently located on theroot of a building, an open sump tends to collect dust, smoke,

soot, insects and other'fo'reign material whichmustbe periodically removed from it in order to prevent fouling of the spray system. A layer of algae frequently builds up in an open sumpcofv a conventional evaporative heat exchangerwhich can be removed only with" greatdiffi- .culty and which tends to foul the pumpsv and piping in the system. c

It is, therefore, desirable to provide. some means of maintaining a uniformly thin film of liquid on substantially the entire surface ofan evaporative heat exchanger employ an evaporative heat exchanger. In an evaporative heat exchanger a heat exchange medium is flowed across the exterior of the heat exchange pipes. Since a substantial quantity of heat must be added toany liquid in order to vaporize-it, .heatmay be removed from the fluid on the interior. of the pipes by conduction through the pipe'walls and be carried away from the heatuexchanger byvaporizing the liquid heat-exchange medium which is flowed across the exterior-of the pipes. 7

Typicalievaporative heat exchangers of pr iorlart con- H 'struction employ spraysystems or. othertmeansffor' dis" chargingaguantity of liquid over the exterior surfacesofa heat exchangerrln order to scure maximum heat transfer capacity, it is desirable tomaintain the entire exterior a surface of the heat exchange tubes'wetted with. a thin film of exterioriliquidqheat.exchange medium such as "waterlf If substantiallygthe entire exterior surface of the Theat exchange tubes isnot wetted, dry areaswill be pres- .ent onthetubesor on the .fins where only convective heat V transfer maytake place-and at which the advantages of hand, if too f great a qua'ntity of jli'quid isr flowed I over-the ?evaporativeheattransfer may not. be obtained due tothe surface of the'lheat' exchange tubesga thick layer of liquid unay be built u'pon the (tubesand fins which will tend to --insulate the tube andactually inhibit heattransfen. I

In atypical heatexchangerconstructionyemploying a .1spray'system tori discharging droplets. 'of water over the exterior surface "of. a heat exchange tube, the surface tensionao the liquidtends tornake the liquid coalesce .into auurnber' of discrete dropletsgon the surface of the I tubeandfins; The droplets possess the disadvantage of E being relatively thick;.and1at the same. time,}thej areas between the 'dropletstend. to bexdry. vAnother disadvan- -F RE without the necessity for employing an;open sump :or a

spray system withtheir attendant disadvantages.

' Accordingly, it is an object of this invcntion'toyprolv ni p ho otmakin an eva t exchanger. s M

V This 'and otherobjects are achieved in thefjembodiment shown by providing a plurality of hollowjporous metal fins about one or more pipes; which forman'evapo'rative heat exchanger. A liquid heat exchange medium such as water is flowed into the interior of the hollow fins and due to theirporosity is'allowed to seep from the interior ofthe fins to theexterior thereof where it; isconstantly available for evaporation By this means substantially the entire porous exterior surface of the hollow metal: fins niay be continually wetted with a thin film' of liquid.

thereby providing maximum capacity for a heat exchanger 5 f'ofthis type.. j v I F ,j A heat exchanger, of the type described'may'be made {rolling a porous sheet of compacted metalpowder and I stamping therefrom-a plurality, of lipped walls. fTh elipped walls Irnayf then 'be assembled with alternatevlips facing. .each other on1aheat exchangetube to "form a hollow {finnedfheat-transfersurfacel Adjacent. lips may. then be sealed together by furnace brazing o'r othe r appropriate means to form apluralitylof hollow fins disposed about the surfaceofthe-heat exchange pipes. 1

he'se and 0th robje'cts. offth' invention will become apparent by reference foflthe following 'specificatipri and attached drawings whereinzf' YfFIGURI E l is aside view partially broken ing an evaporative heat exchanger constructed in" accordance-withthis invention mounted on the roof of abuilding; Y

FIGURE 2 is a cross-s'ectional view taken substantially 3 illustrates a method ofzsealing the'l-ip poftions of the walls of heat exchange fins made in accordance with the described method.

Referring particularly to FIGURE 1, a heat exchanger in accordance with this invention is shown mounted on supports 18 which may hold the heat exchanger in a slightly tilted position on the roof of a building. it will be understood that for purposes of illustration the heat exchanger described. is adapted to be employed as an evap orative condenser on the exterior of a building. However, other applications ofsuch a heat exchanger will be readily apparentto those skilled in the art. For example, a heat exchanger of the type described is particularly suited to location within the interior of a building because of the elimination of a spray system and consequent entrainment problems.

Heat exchanger 10 comprises a plurality of heat exchange tubes or pipes 11 having disposed thereon a plurality of fins 12. Pins 12 each comprise a first porous wall 13 and a second porous wall 14 as can best be seen in FIGURE 2. Porous walls 13 and 14 are desirably made of a compacted metal powder having good thermal conductivity characteristics such as copper. Walls 13 and 14 may be generally fiat sided as shown in FIGURE 2 or if desired they may be corrugated. Edge portions 31, 32 and 33 are provided with lips which are bent out of the plane of walls 13 and 14 and which have a narrow flat portion for engagement with a corresponding lip of another wall. Wall 13 is preferably identical to wall 14 and engagement between corresponding lip portions is secured by reversing alternate walls comprising the fins and positioning them so that the fiat portions of lips 15 are closely adjacent each other as shown in FIGURE 2. Appropriate holes are formed in walls'13 and 14 for accommodation of impervious heat exchange pipes 11 such as copper which pass therethrough.

Eachpair of adjacent lips 15 form and are sealed to each other on three edges 31, 32, and 33 of fin 12. Consequently, fin 12 comprises a hollow envelope 16 having sealed lip portions and spaced wall portions for the accommod'ation of a heat exchange fluid medium such as water therein. The remaining or fourth edge of fins 12 For convenience of manufacture,

may be left substantially open-and communicates with I storage tank where pressure regulation of the fluid in fins 12 is not required.

In operation, heat exchange pipes 11 are connected to the desired supply and discharge conduits of the system With which heat exchanger 10 is to be used. For example, if heat exchanger 10 comprises the condenser of a a refrigeration system, one end of .heat exchange pipes 11 would be connected with the discharge line of acompressor (not'shown) and the other end of heat exchange tube 11 would be connected with the expansion device (not shown) of the refrigeration system. The hot fluid V V such as refrigerant gas'which is to be cooled or condensed flows through the interior of heatexchange pipes 11. A volatile liquid refrigerant such as wateris introduced into the interior. 16 of fins 12'by means of l 1' eader.17.. Since the walls 13 and 14 of fins 12 are.porous,the volatile liquid is enabled to seep bycapillary action through the" walls where it may be evaporated from their exterior surface. As used herein, the term porous refers to the characteristic of a body having alarge number of small internal pores or voids qWhlCli communicate with each other and'with the surface of the body.

Whenin use, heat'is conducted from a fluid in pipes-11 that pairs of the lips are relatively'closely adjacent or in contact with each other. If the fins are relatively thin,

through the walls of the pipes to the walls 13 and 14 of fins 12. Since the material of pipes 11 and fins 12 is preferably a relatively good heat conductor, a relatively low resistance thermal path is established to dissipate heat from pipes 11. Heat reaching the surface of fins 12 is absorbed by the film of water-or other volatile liquid on the surface'of the fins and the liquid vaporizes. The vapor then escapes into the ambient atmosphere carrying with it the latent heat of vaporization of the liquid which was removed from the fluid in pipes 11. As the volatile liquid heat exchange medium is vaporized from the exterior of fins 12, additional liquid is supplied to the exterior surface of the fins by capillary action from the interior 16 thereof. Therefore, substantially the entire exterior surfaces of fins 12 are continuously supplied with a thin film of the liquid heat exchange medium which is available for vaporization therefrom.

Heat exchanger 10 may be suitably manufactured by compacting and rolling a powdered metal such as copper having relatively high thermal conductivity. In order to provide rigidity to the sheet of compacted metal, it is desirablethat the sheet be sintered. However, care must be taken not to carry the sintering operation so far that the internal voids in the metal are sealed off from communication with each other or with the surface, or entirely eliminated by this operation.

- The sheet of compacted metal may be then positioned in a hydraulic punch press where walls 13 or 14 of fins 12 are shaped and trimmed. As has been previously described, it is desirable that walls 13 and 14 be identical with each other and merely reversed in respect to each other to form fin 12. At the same time that walls 13 and 14 are formed in the punch press, apertures 23 may be formed for the accommodation of pipes 11. Walls 13 and 14 are then assembled on pipes '11 either by first positioning the walls of fins 12 in a nesting die and thereafter inserting pipes 11 through apertures 23 or by locating pipes 11 in position and sliding Walls 13 and 14 of fins 12 over the pipes. In either event, walls 13 and 14- are positioned to such that the lip portions thereof face in alternate directions so that pairs of the lips are rela tively closely adjacent each other and when subsequently sealed, they will form a hollow envelope shaped fin 12.

In order to facilitate the sealing of lips 15 and to facilitate the creation of a good low resistance thermal 'bond between pipes 11 and fins 12, itis desirable to tin the surfaces which will be joined to each other with solder. For example, pipe 11 may desirably be a copper tube having a tinned surface and the mating surface of lips 15 may be cleaned and fiuxed in an acid bath and thereafter tinned. The assembly of pipes 11 and faces 13 and 14 after being properly tinned may be inserted into a brazing oven 35 which will melt the liquid solder at their contacting surfaces and upon cooling, a rigid and sealed assembly is thereby provided. Alternatively, the assembled sides and pipes maybe salt bath brazed to accomplish a similar result. 13 and 14 are relatively closely adjacent each other in comparison with the distance between lips 15 of adjacent fins 12, another means of sealing edges 31, 32 and 33 would be to dip the edge portions of the fins into a molten bath of solder or plastic and allowing the molten material which accumulates between lips 15 to cool thereby sealing the appropriate edges of fins 12. In each of the described alternatives, it willbe noted that liquid material is permitted to solidify between adjacent lips 15 of the sides of fin 12 to. form a liquid type enclosure or envelope. 7 v

While it is not necessary; to do so, it isconvenient to space each of sides 13. and 14- the same distance apart on pipe '11- and construct lips 15. of anappropriate size so that when the sides are assembled on pipe'11 with the lips placed in alternating directions alongthe tube,

Since lips 15 of faces i this construction will accommodate a large number of that in actual practice the fins may be much narrower than shown in thedrawings. I

Theconstruction illustrated possesses a number of advantages of prior art heat exchangers. For example, since all spray systems and open sumps can be eliminated by this construction, a heat exchanger of the type-described may be located inside a building where the elimination of entrained moisture. might otherwise become a problem. Furthermore, because of the principle of a encountered with prior art evaporative heat exchangers such as the accumulation of dirt and soot or the build up of algaeon the surface of the heat exchanger are completely eliminated.

Another advantage of the construction described is the elimination of the sump, recirculating pump, and spray system which is frequently required in prior art heat exchangers. The elimination of these elements not only reduces the initial cost of the system but tends to make it more reliable and less expensive to maintain because of the reduction in associated system components. In addition, exceptionally fine evaporative heat exchange characteristics are available by use of the construction described because substantially the entire surface of the heat exchange fins may be uniformly wetted with a thin film of volatile liquid thereby overcoming the tendency of external sprays to coalesce into droplets on the surface of the heat exchange tubes and to create regions of thick film and dry regions which unduly limit the capacity of prior art heat exchangers.

While reference has been specifically made to heat exchangers such as evaporative condensers, it should be understood that the principles of this invention are applicable to other heat exchangers as well. If desired a heat exchange construction of the type described may be used as an air conditioning apparatus to humidify, disinfect, or odorize a conditioned area. For example, high humidity or bacteria control may be maintained in a hospital operating room by placing a heat exchanger of this type functioning as an air conditioner in the room Without the danger of entraining moisture in the air. The heat exchanger is then used to vaporize water or a germicide which is supplied to the interior of the hollow fins and a hot fluid may be passed through the heat exchange pipes to vaporize the liquid more rapidly. Various other applications, embodiments and modifications will occur to those skilled in the art and it is to be understood that this invention is not limited to the described embodiments but may be otherwise practiced Within the scope of the following claims.

I claim:

1. A method of making a heat exchanger which comprises the steps of: forming and sintering a quantity of powdered metal into a plurality of porous metal heat transfer members having an aperture therein adapted to receive the exterior surface of a hollow heat exchange pipe, saidheat transfer members, each being formed with lip portions thereon disposed out of a plane of a side in opposite directions'so that the lip portions of the pairs of members are closely adjacent each other; form ing a relatively low resistance thermal bond between said completely closed heat exchanger construction, problems heat transfer member and between the said heat exchange pipe and said members by solidifying a solid material etween the lip portions of pairs of members and between said members and said heat exchange pipe, and thereby also forming hollow porous envelopes disposed about said pipe; and attaching .a header means in communication with said hollow porous envelopes to introduce a volatile liquid into the interior of said hollow porous envelopes to enable wetting of the exterior surface of said envelopes from the interior thereof through said porous members, whereby evaporation of said liquid may take place from said exterior surface.

2. A method of making an evaporative heat exchanger which comprises the steps of: forming a plurality of porous metal heat transfer members, each having a'relatively large number of internal pores in communication with each other and with the surfaces of the members, by compacting powdered metal into a desired shape; sintering the compacted powdered metal members to form rigid metal heat transfer members while maintaining the relatively porous structure thereof; forming a plurality of apertures in said heat transfer members adapted to conform with the exterior surfaces of a like plurality of tubular heat exchange pipes; forming lip portions disposed out of the plane of a side of said heat transfer members; assembling said heat transfer members on a plurality of hollow, impervious, metal heat exchange pipes with one of said pipes extending through each of said apertures, said heat transfer members being alternately reversed so as to be positioned in pairs with the lips of said pairs of said members being positioned closely adjacent to each other; forming a relatively low resistance thermal bond between said heat transfer members and between said heat exchange pipes and said members by solidifying a fluid material between lip portions of pair of members on substantially only three sides thereof and thereby also forming a plurality of a sealed, hollow envelopes for the reception of a volatile liquid; and attaching a header in communication with said hollow porous envelopes to introduce said volatile liquid into said envelopes through the unsealed side thereof to thereby enable wetting of the exterior surfaces of said hollow envelope through the porous heat exchange members from the interior thereof and evaporation of said liquid from the exterior of said envelope.

References Cited by the Examiner UNITED STATES PATENTS 1,730,064 10/29 Eskilson 113-118 X 2,211,813 8/40 Franceo-Ferreira 29157.3 2,401,483 6/46 Hensel et a1. 29-1912 X FOREIGN PATENTS 7,681 1905 Great Britain.

WHITMORE A. WILTZ, Primary Examiner.

JOHN F. CAMPBELL, Examiner. 

1. A METHOD OF MAKING A HEAT EXCHANGER WHICH COMPRISES THE STEPS OF: FORMING AND SINTERING A QUANTITY OF POWDERED METAL INTO A PLURALITY OF POROUS METAL HEAT TRANSFER MEMBERS HAVING AN APERTURE THEREIN ADAPTED TO RECEIVE THE EXTERIOR SURFACE OF A HOLLOW HEAT EXCHANGE PIPE, SAID HEAT TRANSFER MEMBERS, EACH BEING FORMED WITH LIP PORTIONS THEREON DISPOSED OUT OF A PLANE OF A SIDE OF SAID HEAT TRANSFER MEMBERS; ARRANGING AND ASSEMBLING SAID POROUS METAL HEAT TRANSFER MEMBERS ON A RELATIVELY IMPERVIOUS HOLLOW HEAT EXCHANGE PIPE PASSING THROUGH SAID APERTURES, SAID MEMBERS BEING POSITIONED IN PAIRS WITH THE LIP PORTIONS OF THE PAIRS OF MEMBERS DISPOSED IN OPPOSITE DIRECTIONS SO THAT THE LIP PORTIONS OF THE PAIRS OF MEMBERS ARE CLOSELY ADJACENT EACH OTHER; FORMING A RELATIVELY LOW RESISTANCE THEREMAL BOND BETWEEN SAID HEAT TRANSFER MEMBER AND BETWEEN THE SAID HEAT EXCHANGE PIPE AND SAID MEMBERS BY SOLIDIFYING A SOLID MATERIAL BETWEEN THE LIP PORTIONS OF PAIRS OF MEMBERS AND BETWEEN SAID MEMBERS AND SAID HEAT EXCHANGE PIPE, AND THEREBY ALSO FORMING HOLLOW POROUS ENVELOPES DISPOSED ABOUT SAID PIPE; AND ATTACHING A HEADER MEANS IN COMMUNICATION WITH SAID HOLLOW POROUS ENVELOPES TO INTRODUE A VOLATILE LIQUID INTO THE INTERIOR OF SAID HOLLOW POROUS ENVELOPES TO ENABLE WETTING OF THE EXTERIOR SURFACE OF SAID ENVELOPES FROM THE INTERIOR THEREOF THROUGH SAID POROUS MEMBERS, WHEREBY EVAPORATION OF SAID LIQUID MAY TAKE PLACE FROM SAID EXTERIOR SURFACE. 